(1) Field of the Invention
The present invention relates generally to the dyeing of textiles and, more particularly, to low toxicity, biodegradable common salt substitutes for use in dyeing of cotton and cotton blended fabrics.
(2) Description of the Prior Art
Cellulose dyeing requires large quantities of common salts, e.g. sodium or potassium salts of mineral acids such as sodium chloride or sodium sulfate, as an aid in dyeing the fiber. The amount of salt may range from 5 up to 125% on weight of goods (OWG). Recently, it has been determined that the sodium and the chloride and/or sulfate content of textile wastewater can be a primary source of pass-through aquatic toxicity in industrial and municipal discharge of treated wastewater. This is because there is no known commercially viable process to remove the dissolved salts from the treated water prior to returning the treated wastewater to the natural waterway. In North Carolina alone, 40% of all wastewater is from textile mills. As a result the amount of salt water being continually discharged into the natural, fresh water receiving streams is increasing. Unfortunately, most fresh water organisms find salt toxic over certain concentrations.
Alkaline earth salts, such as magnesium carbonate, offer an alternative to sodium salts for textile dyeing. This is because the alkaline earth salts are lower solubility compounds compared to sodium chloride or sodium sulfate and, due to their chemical nature, can be removed by precipitation during treatment of wastewater from the dyeing process. The solubility of the alkaline earth salts can be further reduced by increasing wastewater pH, resulting in the formation of alkaline earth hydroxides.
A comparison of the solubility of sodium and magnesium compounds in water at 20 degrees C can be summarized as follows:
Sodium Chloride: &gt;350 g/1 PA1 Sodium Sulfate: &gt;275 g/1 PA1 Magnesium Sulfate: 71 g/1 PA1 Magnesium Acetate: &gt;100 g/1 PA1 Magnesium Carbonate Hydroxide: Insoluble
Unfortunately, most alkaline earth salts also usually precipitate under neutral or slightly alkaline conditions and can cause severe hard water deposits. Thus, the use of these non-sodium, potassium and ammonium compounds has been limited to the acidic conditions found during the rinsing or after fixation steps in the dyeing process.
For example, it has been known for some time that alkaline earth salts can act as a dyestuff antimigrants in textile dyeing. One such compound is sold by ICI America under the tradename DRILEV JH for the prevention of migration in direct dyeing. DRILEV is a solution of magnesium acetate with about 10% excess acetic acid. However, there has been no suggestion of using DRILEV as a salt substitute. Furthermore, the recommended use pH for DRILEV is about 3.0 to 5.0 which is too low for satisfactory dyeings.
In order to be commercially acceptable, a salt substitute must be easy to use in place of conventional salts. Accordingly, the salt replacement must exhibit long term storage stability and dye satisfactory at any conventional operational dyebath pH. In addition, the salt should not precipitate at conventional dyebath concentrations or cause deposits on the goods. Thus, the useful pH range of the salt substitute needs to be from 5.5-12.0.
The alkaline pH stability of the product is also important when dyeing fiber reactive dyes, which are fixed or reacted with the cellulose under alkaline conditions. Direct dyes are fixed or exhausted under ambient pH conditions or slightly adjusted pH conditions which are not as severe as the alkaline conditions found in fiber reactive dyeing.
Thus, there remains a need for a low toxicity, biodegradable salt substitute for use in dyeing of cotton and cotton blended fabrics which is efficacious in the dyeing of cellulose fiber, non-toxic in the aquatic environment and can be precipitated to produce a biodegradable organic anion.